In recent years, aqueous polymer dispersions prepared by emulsion polymerization, for example, of acrylonitrile-styrene, vinyl acetate, ethylene-vinyl acetate, and the like have been increasingly used as paints, adhesives, and so forth. These conventional aqueous polymer dispersions, however, have a serious problem in that they can only provide coating films which exhibit poor adhesion to metals, wood, cement-hardened products, plastics, and so forth, and which are often subject to peeling and blistering, particularly under wet conditions or at high temperatures. In order to solve the problem, several attempts, such as reducing the amount of water-sensitive substances, e.g., surface active agents and protective colloids, contained in the aqueous polymer dispersion, and formation of a cross-linked structure by the introduction of functional groups into the polymer skeleton (see U.S. Pat. Nos. 3,991,216, 4,065,415, 4,065,416 and 4,097,438), but with insufficient effects.
In addition, an attempt to improve the water resistance of coating film by addition of thermosetting resins, such as epoxy resins, in combination has been made (see Japanese Patent Application (OPI) No. 78237/78) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). This method, however, suffers from disadvantages in that the epoxy resin separates from the polymer component during storage, coating films obtained become turbid, and the water resistance of the coating film is insufficiently improved.
In order to overcome the above-described defects, Japanese Patent Application (OPI) No. 1228/78, for example, has disclosed a method in which an epoxy resin is grafted onto a carboxy group-containing acryl polymer to prepare a graft copolymer having a selfemulsification capability, and the graft copolymer is dispersed in water. This method also suffers from disadvantages in that the graft efficiency is poor, and therefore the grain size of the graft copolymer to be dispersed in water is large, making it difficult to control the flow and extension of the resultant dispersion product. Furthermore, the water dispersion stability is poor unless the ionization ratio of the carboxy group is high.
It has therefore been desired to develop aqueous dispersion compositions which overcome the above-described defects of the prior art technique, and provide coating films having excellent water resistance, solvent resistance, and physical properties.
Industrial adhesives which are now widely used are generally thermosetting resin-based and emulsion-based adhesives. Non-solvent type adhesives have also long been used. Adhesives prepared using chloroprene rubber as a starting material are almost all solvent type adhesives, and therefore, in view of safety and sanitation, it is strongly desired to produce aqueous chloroprene rubber-based adhesives.
Solvent type adhesives prepared using chloroprene rubber have advantages in that the contact properties are good, the initial adhesive force is strong (because of high crystallinity), and the heat resistance and water resistance are good. Thus, they have many uses, for example, in wood-working and automobile production. Emulsion type adhesives are inferior in the initial adhesive force, heat resistance, and water resistance compared to the solvent type adhesives. In order to overcome these defects, therefore, various proposals have been made, but satisfactory adhesives have not yet been obtained.